1. Technical Field
The present disclosure relates to a field control system. More particularly, the present disclosure relates to a filed control system that includes a field controller connected to a control network and executes computation processing for controlling a field device according to a given control cycle while executing a data communication between the field controller and the field device.
2. Related Art
In the field control system, a field device is connected to a field controller through an input and output module, and the field controller repeatedly executes computation processing necessary for field control while executing data input and output processing with the field device according to a given control cycle. This computation processing is performed using the input data obtained from the field device, and the result of the computation processing is reflected in the output data to the field device (see e.g., JP-A-2006-276958).
However, in the case where the computation processing and the data input and output processing are executed by one processor, the processing of the processor is monopolized during the data input and output processing with the field device and this reduces the overall performance of the system.
On the other hand, it is considered to use a dedicated coprocessor for the data input and output processing with the field device. In this case, the coprocessor can perform the processing of data from the field device at all times independently of the processing of the processor. When receiving a data output request from the processor, the coprocessor suspends the data input processing and executes data output. By such a processing procedure, the processing amount of the processor is significantly reduced, whereby the overall performance of the system can be improved.
However, since the processor cannot control the timing of the data input processing, the data input timing varies. Thus, there may be a problem in that the processor obtains old data.
Moreover, when communication is performed between a plurality of field controllers connected to the control network, if the timing of the data input processing or the like differs among the field controllers, problems arise in that the accuracy and stability of control are reduced.